As a conventional auxiliary power source device for a vehicle, for example, in an auxiliary power source device for a vehicle described in Patent Literature 1 mentioned below, there is disclosed a configuration in which a PWM converter is connected to an output terminal of a main transformer that transforms and outputs an alternating current (AC) input from an AC overhead wire, a three-phase inverter is connected to an output terminal of the PWM converter, and a filter circuit for eliminating a harmonic component included in an output voltage of the three-phase inverter is included in an output terminal of the three-phase inverter.
The filter circuit mentioned above is configured to include three AC reactors that are respectively inserted in three-phase output lines connecting the three-phase inverter and a three-phase load such that one end is connected to the output terminal of the three-phase inverter and the other end is connected to the three-phase load, and three filter capacitors that are respectively drawn out from three-phase output lines positioned on the other end side of the respective AC reactors and connected to each other in a Y shape, and a connection point of each of the other ends as a neutral point of the Y-connection is grounded.